Adult chronic disease is the major public health problem of both the industrialized and developing world today. Although typically associated with aging and health of the elderly, there is mounting evidence that chronic conditions are beginning at younger ages in the US. This subproject brings together complementary and comprehensive expertise of program project investigators in an innovative collaborative integration of the diverse multilevel data collected in the Wave V Program Project with earlier longitudinal Add Health data: 1) to document the prevalence of preclinical chronic disease risk and frank disease in young adulthood, and 2) to evaluate evidence supporting three life course models of chronic disease emergence within the Developmental Origins of Health and Disease (DOHaD) paradigm, including the Latent Effects Life Course Model, the Cumulative Model, and the Pathways Life Course Model. Add Health data are uniquely suited to address these aims because the study encompasses a large, diverse, representative sample with rich repeated measures (survey and biomarker based) of health and health behavior, longitudinal characterization of social and physical environments, and experiential information from gestation across the life course. Descriptive analyses will include production of derived (e.g., BMI) and constructed variables (e.g., allostatic load) from Wave V and earlier waves, and documentation of population levels of chronic disease risk and incidence and prevalence of disease according to key demographics such as biological sex, race/ethnicity, SES, and geographical region. Evaluating DOHaD models will entail multiple approaches suited to address their respective hypotheses, including structural equation modeling and latent class growth models to cluster respondent-specific trajectories by type. Models will incorporate individual time-varying risk indicators and aggregated indices of cumulative risk. Completion of these aims will transform knowledge on the additive and interactive pathways leading to chronic disease by linking young adult health and disease risk to physical and social exposures that occur during gestation, childhood, and adolescence, with vital implications for prevention and intervention efforts.